The present invention relates to an electronic still camera, and more particularly, to an electronic still camera wherein an image obtained through an image pickup lens is received by a solid-state image pickup element so that a still image is handled as digital data.
An electronic still camera is structured so that an image obtained through an image pickup lens is subjected to photoelectric transfer in a solid-state image pickup element, and image signals thus obtained are handled as digital data.
In the case of a camera employing a solid-state image pickup element (a still camera handling a still image and a video camera handling a moving image), it has so far been known, when a resolving power is high to be at a certain level or higher and a subject is a cyclic one such as a net pattern, that an interference is caused by the cyclic relation of intervals of photosensors of the solid-state image pickup element, and a false image is generated.
There have been utilized double refraction characteristics of an optical low-pass filter made of crystal plate to double an image and thereby to cut high frequency components by lowering the resolving power of the image pickup lens to prevent occurrence of the problem of the false image mentioned above.
(1) First problem
However, there has recently been an increasing demand for higher image quality, and it has been found that an image obtained by using a conventional optical low-pass filter alone can not satisfy the demanded image quality sufficiently.
On the point of high image quality, in particular, it has been demanded to make an image of an electronic camera to be close to that of silver halide photography, and there are demands not only for resolving power but also for image sharpness and contrast (definition).
(2) Second problem
(1) In photoelectric conversion characteristics of a solid-state image pickup element, a change in output for a change in input is greater than in the case of gamma characteristic of a silver halide film. PA1 (2) Even when the same quantity of light arrives at a photosensor portion of a solid-state image pickup element, the rate of photoelectric conversion varies depending on an incident angle. PA1 (3) FIG. 11 shows a section in the horizontal direction of a pixel, and eclipse is caused on the peripheral portion of a solid-state image pickup element depending on an incident angle, by an uneven surface on the peripheral portion of a photosensor (light-receiving portion) of the solid-state image pickup element such as that shown in FIG. 11. For a certain incident angle, therefore, light arrives at a photosensor portion located at a recessed portion, and the rate of photoelectric conversion is lowered. An influence of this phenomenon is greater on the peripheral portion of the solid-state image pickup element.